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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 107, NO. B6, 2106, doi:10.1029/2000JB000057, 2002

Equivalent channel network model for permeability and electrical conductivity of fracture networks

Clinton D. Van Siclen

Idaho National Engineering and Environmental Laboratory, Idaho Falls, Idaho, USA

Abstract

It is remarkable that the permeability k and electrical conductivity σ of saturated, fractured rock exhibit a power law relationship with exponent r as pressure is applied to the rock. To understand this behavior, the fracture network is viewed as a collection of connected, planar fractures. This allows the construction of algebraic expressions for the transport properties of the fracture network, in which the local effective properties, namely, the hydraulic aperture d_h and the electric aperture d_e of the representative planar fracture (the “equivalent channel”), are distinguished from the network properties (e.g., fracture connectivity) parameterized by the tortuosity factors τ_h and τ_e. This “equivalent channel network model” reproduces the observed power law behavior on the conditions that d_h³ ∝ d_e^r and τ_h ∝ τ_e^r over the range of applied pressures. The first condition is met, as demonstrated by calculations for a variety of simulated planar fractures using the Reynolds equations for fluid and current flow. The value of the exponent r is found to indicate the degree to which the fracture resembles a porous medium but cannot otherwise identify fracture surface or aperture characteristics. No direct evidence currently exists to support the second condition; however, such a power law relationship has been demonstrated elsewhere for simulated porous media.

Published 4 June 2002.

Index Terms: 5104 Physical Properties of Rocks: Fracture and flow; 5139 Physical Properties of Rocks: Transport properties; 5109 Physical Properties of Rocks: Magnetic and electrical properties; 1829 Hydrology: Groundwater hydrology.

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Citation: Van Siclen, C. D. (2002), Equivalent channel network model for permeability and electrical conductivity of fracture networks, J. Geophys. Res., 107(B6), 2106, doi:10.1029/2000JB000057.

Copyright 2002 by the American Geophysical Union.